Abstract
The interleukin-3 (IL-3) receptor is a cell-surface heterodimer that links the haemopoietic, vascular and immune systems and is overexpressed in acute and chronic myeloid leukaemia progenitor cells. It belongs to the type I cytokine receptor family in which the α-subunits consist of two fibronectin III-like domains that bind cytokine, and a third, evolutionarily unrelated and topologically conserved, N-terminal domain (NTD) with unknown function. Here we show by crystallography that, while the NTD of IL3Rα is highly mobile in the presence of IL-3, it becomes surprisingly rigid in the presence of IL-3 K116W. Mutagenesis, biochemical and functional studies show that the NTD of IL3Rα regulates IL-3 binding and signalling and reveal an unexpected role in preventing spontaneous receptor dimerisation. Our work identifies a dual role for the NTD in this cytokine receptor family, protecting against inappropriate signalling and dynamically regulating cytokine receptor binding and function.
Highlights
The interleukin-3 (IL-3) receptor is a cell-surface heterodimer that links the haemopoietic, vascular and immune systems and is overexpressed in acute and chronic myeloid leukaemia progenitor cells
The IL-3 receptor system has come under the spotlight because stem/progenitor cells from patients with acute myeloid leukaemia (AML) overexpress the IL-3 receptor α-subunit (IL3Rα) and this is associated with reduced patient survival[3,6,7,8,9]
We have determined the crystal structure of IL-3 bound to its receptor α-subunit, IL3Rα, to 2.7-Å resolution (Methods, Table 1, Fig. 1, Supplementary Fig. 1)
Summary
The interleukin-3 (IL-3) receptor is a cell-surface heterodimer that links the haemopoietic, vascular and immune systems and is overexpressed in acute and chronic myeloid leukaemia progenitor cells. It belongs to the type I cytokine receptor family in which the α-subunits consist of two fibronectin III-like domains that bind cytokine, and a third, evolutionarily unrelated and topologically conserved, N-terminal domain (NTD) with unknown function. IL-3 is a member of the beta common (βc) cytokine family, which includes granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5 These cytokines signal through heterodimeric cell-surface receptors that are expressed at low levels and comprise a cytokine-specific α-subunit and the shared βc subunit[1]. A molecular explanation for how a single mutation converts IL-3 into a superkine has not been forthcoming
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